MEMS ribbon devices are used in several kinds of high speed light modulators including grating light valves, interferometric MEMS modulators, MEMS phased arrays, and MEMS optical phase modulators. Each of these light modulator technologies may be employed in personal display, projection display or printing applications, as examples.
MEMS ribbons are made in a variety of shapes and sizes depending on the specific application for which they are designed; however, a typical ribbon may be roughly 50-350 microns long, 2-10 microns wide, and 0.1-0.3 microns thick. Ribbons are suspended roughly 0.2-0.5 microns apart from a substrate to which they may be attracted through the application of an electric field. Ribbons of these approximate dimensions are capable of moving between rest and deflected positions in as little as a few tens of nanoseconds.
The high speed of MEMS ribbon devices has led to display designs in which a linear array of ribbons modulates a line image that is scanned across a viewing area. The ribbons move so fast that a linear array of them can create a sequence of line images to form a two-dimensional image without any perception of flicker by a human observer. Modulating light with linear, rather than two-dimensional, arrays also leads compact modulators that make efficient use of valuable silicon chip real estate.
MEMS linear-array light modulators are thus attractive candidates for integration with CMOS manufacturing processes. A MEMS linear-array may even be considered to be an optical output stage for an integrated circuit. Many CMOS electronic driver chips operate with unipolar supply voltages, however, and unipolar drive does not always work well with ribbon devices. In extreme cases ribbons driven from a unipolar power supply fail to respond after just a few minutes of operation.
What are needed, therefore, are robust methods to drive MEMS ribbon devices using unipolar power supplies so that ribbons and CMOS electronics can be tightly integrated.